Apparatus for scoring synthetic plastic sheet material

ABSTRACT

Apparatus for forming a score line of predetermined configuration in synthetic plastic sheet material includes a female die member having a slot corresponding to a desired score line, a male scoring member including a scoring rule movable against the sheet material to stretch it into the slot, and a resilient material frictionally engaging the sheet to immobilize the sheet between the members in those areas bordering the slot during score-forming. The resilient material extends along opposite sides of the rule and above its operable end. In one embodiment, the scoring member is of sufficient dimension to extend into the slot and compress the sheet material between the slot&#39;&#39;s bottom and the end of the scoring rule.

FIGS. 2 to 4 are reduced simplified plan views of the FIG. 1 apparatus showing the rolls and turning rods re spectively in the 90 and 180 position; I

FIG. is a side elevation corresponding to FIG. 1 but of a second embodiment of reciprocating rotary apparatus in the basic or zero degree position;

FIG. 6 is a detail of the F IG. 5 embodiment as viewed in the direction of the arrow VI in FIG. 5;

FIG. 7 is a sectional detail taken on the line VII-VII in FIG. 5;

FIG. 8 shows a different embodiment of a reversing apparatus according to theinvention;

FIG. 9 shows of the embodiment'of FIG. 8 a detail which corresponds to that of FIG. 6;

FIG. is a diagrammatic view showing a further modification; and

FIG. 11 shows of the embodiment of FIG. 10 a detail which corresponds to that of .FIG. 6.

An extruder- (not shown) having a blowhead (not shown) forms a tubular film l which is flattened by flattening plates 2 that are fixed to an auxiliary frame 3. The auxiliary frame is carried by a cross-member 4 on a supporting shaft 5 which is rotatably mounted in the main frame 6 of the apparatus. The frame 6 includes columns 7 supported on a take-off platform 8 having an aperture 9 in line with the shaft 5. The flattening apparatus comprising the plates 2, auxiliary frame 3, crossmember 4 and shaft 5 is rotated by means of a gear motor 10 of which the direction of rotation is reversed after every 360 by any suitable means such as stationary electric end switches.

The flattened film is passed in S formation about two squeeze rolls l1 and 12 and a guide roll 13 which is carried by a holder 13 in the auxiliary frame 3 and which therefore participates in the reversed 'or reciprocating rotary motion of the auxiliary frame. It has been found that looping of the film in S formation about the rolls 1], l2 achieves adequate squeezing of the film so that no air can escape from the tubular portion into the flattened portion of the film. Since there is thus no intense pressure as would be applied during flattening of the film with conventional squeeze rolls, it will be particularly advantageous if the two rolls 12, 13 are in the form of water-cooled rolls because the film passes about these rolls in opposite senses and through precisely 180 so that both sides of the film are cooled to the same extent. The supply and withdrawal conduits for the cooling water constitute the only flexible energy supply connections that are necessary for the apparatus of the invention and this helps to ensure efficient operation.

Downstream of the guide roll 13 and pivotably mounted to one side of the supporting shaft 5 there are a first turning rod 14 and its mounting l5 and bearing sleeve 16, a direction-changing roll 17 with its mounting 18 and bearing sleeve 19 and a second turning rod 20 with its mounting 21 and bearing sleeve 22. All these rods are tangential to imaginary circles concentric with the central axis of the supporting shaft 5. The

required spacing or radius will be described later.

As diagrammatically indicated'in FIGS. 2 to 4, the direction-changing effect for the film results from the fact that between the successive direction-changing rolls and turning rods 13, 14, 17, 20 and 23/24 an angle of twist is set up corresponding to onequarter of the angle of twist of the auxiliary frame 3 with flattening plates 2 relatively to the stationary frame 6. In the FIG. 1 embodiment the individual rotatable elements are positively intercoupled by gear segments 25, 26 at the respective ends of each bearing sleeve 16, 19 and 22 as well as on the cross-member 4 and on the bearing sleeve 27, these gear segments being engaged by four corresponding double gears 28 which freely run on a shaft 29. The shaft 29 is fixed by a holder 30 to the bearing sleeve 19 of the central direction-changing roll 17 so that the entire gearing'28, 29, 30 effecting positive interconnection and guiding for the required relative rotations will always be disposed in the free space on the angular bisector behind the two turning rods 14,

The spring 31 shown in FIG. 1 is intended to indicate that in order to counteract play in the gears 25, 26, 28 the shaft 29 is preferably spring-influenced so as to avoid dead spots in the gearing. The required ratios for the gears 25, 26, 28 are calculated from the known formulae for planetary gears.

In a modification, only one gear segment 25 is provided on each of the sleeves 16, 19, 22, 27 and the cross-member 4 to engage with a respective single gear 28 on a shaft29 which will in this case be rotatable, the holder 30 and calculation of the gear ratio being the same as already described.

The desired positive coupling for the rotational movements can also be brought about by a lever system in the form of spherically movable lazy tongs, the central pivot points of the tongs lying in alignment above one another when in the basic (zero degree) position at the cross-members 4, the movable bearing sleeves 16, 19 and 22 and the stationary bearing sleeve 27. This construction is illustrated in FIGS. 5 and 6. The hinge holder 32 is mounted on the cross-member 4 to rotate therewith, the hinge holder 33 on the bearing sleeve 16, the.hinge holder 34 on the bearing sleeve 19, the hinge holder 35'0n the bearing sleeve 22 and the hinge holder 36 on the bearing sleeve 27, the attachment being on that side which is remote from the direction-changing rolls and turning rods l3, l4, l7 and 20 so that the film will not be impeded by the levers. The hinge holders 32 to 36 are connected to the lazy tongs which comprise strip levers 37 and 38 and associated connecting hinges 39. FIG. 6 is a simplified drawing showing the elongation of the lever system when the hinge holders 32 to 36 are laterally displaced, the spacing between each pair of hinge holders 32-33, 33-34, 34-35 and 35-36 being one quarter of the lateral displacement of the lowermost hinge holder 32. This path also corresponds to a quarter of the rotary angle. By reason of the twist which the system undergoes during pivoting of the direction-changing rollsof the turning rods, the necessary spherical movability is in the simplest case achieved by making the levers 37 and 38 of relatively wide but thin spring steel strip so that they will follow the twist of the system without collapsing. In contrast with gearing, the lever sytem provides almost play-free positive coupling whereas the above-described first embodiment makes it necessary to take special precau- APPARATUS FOR SCORING SYNTHETIC PLASTIC .SI'IEET MATERIAL This application is a divisional application of my earrial, filed Jan. 31, 1968.

BACKGROUND OF THE INVENTION Basically, two methods have been proposed'for scoring semi-rigid synthetic plastic sheet material. According to one method, a platen or die member having an unbroken surface is adapted to cooperate with a scoring rule member. During score-forming, a sheet of plastic material is interposed between these members and then they are moved together to force the plastic material between the platen and the scoring rules thereby thinning the plastic in those areas. This is commonly called hinging-the hinges are characteristically easy to fold and capable of multiple flexing, i.e. have fatigue resistance. In another method, the platen is provided with a slot defining the score to be formed in the plastic sheet material which cooperates with a male scoring rule during score-forming. In'this latter method, the male scoring rule is moved into the female slot with the sheet material positioned therebetween to cause the plastic sheet material to be scored by the score-forming action of the male and female members.

Both of the proposed methods have proved unsatisfactory for a number of reasons. In the first mentioned method, the score is formed by thinning the plastic material in the area between the scoring rules and platen member. The excess plastic material is pushed off to both sides of the scoring rule and is pushed into the unscored areas of the sheet. As a result, the scored plastic sheet instead of laying flat has a series of bubbles between the score lines. Bubbled, scored sheet material has the disadvantage of not lending itself to efficient stacking or packaging. Moreover, and importantly, stretching or bubbling the plastic material in the unscored areas elongates the sheet material laterally and longitudinally which tends to mitigate any attempt to achieve precise dimensional tolerances in the scored sheet.

Dimensional uniformity and precision in the production of scored and cut blanks are essential. This is demonstrated, for example, in the production of blanks for containers such as milk cartons. The dimensional tolerances in synthetic plastic sheet blanks for the production of milk containers in high speed machinery is on the order of 10.005 inch. According to the mentioned prior art methods, plastic blanks are only capable of being made with dimensional tolerances on the order of about i 0.030. This has been proved intolerable in high speed precision machinery. Lack of dimensional precision in the blank results in inefficient machine operation. Blanks out of tolerance with the machine parts frequently jam up the machine or result in the formation of an undesirably packaged product. For example, lack of dimensional uniformity in the scored blank produces a packaged container where scaling is inadequately effected or where the level of the contents can-' not uniformly be maintained between containers. Also blanks are usually made separately and shippedto the place of use. A relatively flat, unbubbled blank is needed to facilitate packaging for shipment.

The second mentioned prior art technique, while tending to provide better control over the depth of scores than the first mentioned method, still produces a bubbled, non-flat blank. ln short, neither of these methods or apparatus have been found suitable for the production of scored synthetic plastic sheet material which is adaptable for use in high speed machinery for producing containers or cartons. There is a need for a process and apparatus for scoring synthetic plastic sheet material without the production of bubbles or blisters between the score lines and the associated disadvantages.

SUMMARY OF THE INVENTION This invention is directed to a process for forming a score line of predetermined configuration in synthetic plastic sheet material which results in a well-defined score without bubbling or stretching the sheet material in the unscored areas. The process according to this invention includes immobilizing the sheet material in those areas bordering the sides of the sheet area defining the score line and locally stretching the sheet material in the area defining the score line while substantially maintaining the sheet material in the immobilized areas against stretching. This process produces a flat, Y

scored blank with overall dimensional tolerances uniformly maintained within a precision of about :t 0.005 inch. The scored and cut blanks of plastic sheet provided according to this invention have been found especially suitable for use in high speed, precision machinery for the production of cartons such as milk containers.

In a preferred form, the process according to this invention includes providing male and female die members movable into and out of score-forming relation with one another by suitable means. The male member has a scoring rule and a resilient material substantially surrounding the rule and extending above the scoring end of the rule. The resilient material has sufficient resiliency for compression below the rule end when the members are brought into score-forming relation. The

female member has a surface witha slot for receiving the rule during score-forming. The female slot terminatesin a bottom at a predetermined depth and the scoring rule end cooperates with the slot bottom during score-forming to press the plastic sheet material therebetween. A plastic sheet material is scored by interposing it between the die members and then moving the members into score-forming relation to cause the resilient material to frictionally engage and sufficiently immobilize the plastic sheet material under compression against the female surface in those areas bordering the slot. The scoring rule is then introduced into the slot to stretch the sheet material thereinto while substantially maintaining the sheet material in the immobilized areas against stretching to score the plastic sheet. During scoring, the end of the scoring rule and female slot bottom cooperate to restrain the stretched plastic material therebetween. The members are then separated to recover the scored sheet. l

' In the preferred form just described, the plastic sheet is locally stretched and oriented into the female slot and then the scoring rule end cooperates with the slot bottom to contact or press the plastic therebetween. This particular score-forming cooperation of the male rule end with the female bottom issometimes conveniently referred to in the description of this invention as the bottom technique." An alternative embodiment of this invention is herein referred to as the bottomless technique. The term bottomless technique applied to the score-forming cooperation of the male and female members where the plastic material is not pressed or contacted between the male rule end and the bottom of the female slot. Both of these techniques have in common the formation of a well-defined score in syn thetic plastic sheet without bubbling or stretching the sheet material in the unscored areas. Also, in both of these techniques scoring is accomplished by immobilizing the sheet material in those areas bordering the sides of the sheet area defining the score line and locally stretching the sheet material in the area defining the score line while substantially maintaining the sheet material in the immobilized areas against stretching.

The bottom technique is presently preferred over the bottomless technique for several reasons. First, score height is better controlled in the bottom technique. Second, it has been found that when the stretched and oriented plastic is contacted or pressed between the scoring rule and the female bottom, a sharper score line in the plastic is obtained. A sharper score line renders the sheet material more foldable. Third, the scored exterior of a blank (i.'e., blank side formed adjacent the female slot) can be more readily shaped by the bottom technique so as to prevent its nesting with the scored interior (i.e., the blank side formed adjacent the male rule) of another blank when they are stacked. The elimination of nesting or sticking of stacked scored blanks is a particular advantage because blanks are usually supplied individually from stacks into high speed precision machinery which sets each blank up into a carton. If blanks stick together, serious problems are encountered in operating the precision machinery.

When scoring and cutting a blank according to this invention, the male member also has a cutting blade which cuts the sheet material when the male and female members are moved into score-forming relation. Preferably, the resilient material of the male member also extends above the cutting edge of the blade to permit effective immobilization and cutting of the sheet material during score-forming.

It has been found that, when score-forming or scoreforming and cutting a carton blank having multiple score lines according to this invention, the immobilization of the sheet material in the unscored areas between the areas defining the score lines or score lines and cuts should be substantially complete. This process produces a flat carton blank and maintains tolerances on the order of about i 0.005 inch. Moreover, this process produces a well-defined score which is oriented at its apex, due probably to the thinning action and partial orientation occurring during localized stretching, and this configuration folds, breaking along score lines readily and efficiently in setting up the carton.'In addition, the flat scored blanks produced by this process can be easily stacked and packaged for transportation -to the place of use.

Apparatus according to this invention includes means for immobilizing sheet material in those areas 'bordering the sides of a sheet area defining the score line and means for stretching the sheet material in the area defining the line. In a preferred form, the apparatus includes a female die member and a male scoring member movable relative to one another into and out of score-forming relation by suitable means. The female member has a surface with a slot therein defining a score line for receiving the male scoring member during score-forming. The male scoring member has a scoring rule for locally stretching the sheet material into the female slot during score-forming. The apparatus also includes means for immobilizing the sheet material between the male and 'female members in those areas bordering the slot. Preferably, the male scoring member has a scoring rule and a resilient material substantially surrounding the rule and extending above the scoring end of the rule. This resilient material has sufficient resiliency for compression below the scoring end of the rule when the members are brought into scoreforming relation. The resilient material is adapted to frictionally engage and immobilize the sheet material between the male and female members in those areas bordering the female slot during score-forming.

This invention permits scoring by pressure forming synthetic plastic sheet material of the semi-rigid polyolefin plastic type. Suitable polyolefin plastic material includes stock sheet material formed of an aliphatic polymer selected from the group consisting of polyethylene, polypropylene and the like. Polymeric compositions of this type conventionally sometimes include plasticizers, fillers and the like. Other synthetic plastic material includes polymers of vinyl aromatic compounds such as high impact biaxially oriented polystyrene and the like which have heretofore been used in the score-forming art. The thickness of the sheet material can vary and it has been found suitable to employ thicknesses of about 7 to about 27 mils when using sheet material of the polyethylene and polypropylene type, for example.

The drawings further illustrate the method and apparatus for carrying out the invention in the best mode presently contemplated. In the drawings:

FIG. 1 is a flat view of a blank of synthetic plastic sheet material cut and scored according to this invention;

FIG. 2 is a simplified, fragmentary cross-sectional view of apparatus according to this invention with plastic sheet material interposed and ready for cutting and scoring the blank as shown in FIG. 1;

FIG. 3 is a view similar to FIG. 2 with the apparatus in score-forming relation for cutting and scoring;

FIG. 4 is a view of the apparatus of FIG. 3 after the sheet material has been cut and scored;

FIG. 5 is an enlarged fragmentary view of a scored area shown in FIG. 3.

Referring to FIG. 1, a synthetic plastic sheet material 10 is shown, cut and scored from a piece of stock material using apparatus 11 of this invention as shown in FIGS. 2-4. The apparatus 11 includes a female die member 12 and a,male scoring member 13 movable relative to one another into score-forming relation by suitable means not shown. These members 12 and 13 can be relatively planar die platens or platens having an arcuate contour as conventionally provided in the rotary die cutting and scoring art. The female die member 12 has a metal or rigid surface 14 with a slot 15 formed therein defining a score line 16 to be formedin the synthetic plastic sheet 10. The slot 15 with bottom 17 is adapted for receiving the male scoring member 13 during score-forming.

The male scoring member 13 has mounted thereon metal or rigid scoring rules 20 and a resilient material 21 substantially surrounding the -rules. The scoring ends of rules 20 are adapted for score-forming cooperation with the bottoms 17 of female slot 15. Also, a cuttingblade 22 is mounted on the male member for cutting the sheet stock during score-forming. As shown, the resilient material 21 extends above the ends of scoring rule 20 and blade 22; and has sufficient resiliency for compression below these ends when the members l2, 13 are brought into score-forming relation. The resilient material 21 extends above the end of rule 20 to a height of about several mils depending upon the depth of the score to be made, the sheet material being scored and its thickness, and the resiliency of the material 21 being used. The resilient material 21 is adapted to frictionally engage and immobilize the sheet material between the members 12, 13 in those areas bordering the slot 15.

When a blank is formed as shown in FIG. 1, male scoring rules 20 and blade 22 are shaped and located to provide the scored lines 16 and cut end 23 of sheet material 10. In the complete apparatus (not shown) for forming a blank, the resilient material 21 substantially surrounds the scoring rules 20, completely between rules 20 and blade 22, for sufficient immobilization of the plastic material in the unscored areas between members 12 and 13.

In carrying out the process according to this invention, a synthetic plastic sheet material of the semi-rigid polyolefin type is interposed between the male and female members 12, 13. For example, a polyethylene sheet material having a thickness of about mils is introduced between the members 12, 13 and then they are moved into score-forming relation to cause the resilient material 21 to frictionally engage and sufficiently immobilize the plastic sheet material under compression against female surface 14 in those areas bordering slot 15. In forming the blank of FIG. 1, the sheet material in the unscored areas 25 or areas between scores or cuts and scores is sufficiently immobilized completely between rules and blade 22 and surrounding the borders of the female slot 15. Then, the scoring rule of the male member 12 is introduced into slot 15 to locally stretch the sheet material while the resilient material 21 substantially maintains the sheet material in the immobilized areas against stretching to score the plastic (shown best in FIG. 5 FIG. 5

" illustrates the bottom technique embodiment of this invention where the ends of rules 20 cooperate with the slot bottom 17 to contact or press the plastic therebetween which is presently preferred for the reasons discussed above. During scoring, the blade 22 cuts the sheet material. The members 12, 13 are then separated, the resilient material recovers its form and the blank is removed.

As shown in FIG. 5, this apparatus and method produces a well-defined score which is oriented at its apex. This bottom technique gives a sharper score line probably due to the stretched plastic being compressed at about its apex with redistribution or shaping of the plastic to render it muchmore foldable. This shaping of the score exterior (i.e., illustrated in FIG. 5 as'tending to flatten" the score apex at slot bottom. 17) also prevents nesting with score interior (adjacent male rule) of slightly different shape when blanks are stacked. In this connection, such a well-defined score is obtainable with thicknesses of sheet material of about one-half of the difference between the width of the slot and the width of the scoring rule. Score height is controlled by predetermining the depth of the slot for co-action with the scoring rule end. It has been found, for example, with polyethylene sheet of about 15 mils in thickness to preferably provide a slot depth which furnishes a score height of about 6 to about 9 mils (as measured between the Hat, unscored surface of sheet side adjacent the female surface to the apex of the score). In the bottomless technique it is also desirable to achieve score heights of about 6. to 9 mils for about 15 mil polyethylene sheet thicknesses as in the bottom technique. It has been observed that as score height increases in the bottomless technique for this same type sheet material to about l5 mils or above that the score lines are less sharp and this excessive height promotes nesting between scored blanks. The latter is probably due to better conformance between the external and internal score apexes of stacked blanks which tends to enhance sticking.

FIG. 5 also shows the score occurring locally in the area of the sheet material defining the score lines while the major flat areas of the sheet were restrained from movement during the scoring action. As mentioned, this provides a relatively flat blank which is not bubbled and does not have accumulations of plastic material at the hinges adjoining the scored areas.

Resilient material which has been found suitable to frictionally engage and immobilize the sheet material between the female andmale scoring members is of the elastomeric or rubber-like type. One form of material includes a cork-rubber o-r elastomeric composition having a hardness of about 233-237 as measured by the Pusey and Jones method. The frictional engagement of the resilient material with the synthetic plastic sheet which is being scored is such that the sheet is sufficiently immobilized in the unscored areas against stretching. Therefore, the coefficient of friction to achieve this type of immobilization will vary depending upon the resilient material and the synthetic plastic sheet being scored. It has been found that cork-rubber composition of the above hardness having a coefficient of friction of about 0.65 to be suitable with polyethylene sheet material. This coefficient of friction was determined by a spring scale sled measurement of sliding friction in which force applied was about 25 lbs. per sq. in. The coefficient of friction was determined by the ratio of the force required to move the polyethylene sheet material over the cork-rubber material to the total force pressing the two together according to the formula k= F W; where F is the force required to move one surface over the other and W is the force pressing the surfaces together.

It is to be understood that there are other modes of carrying out the invention which are within the boundaries of this description and the skill of the art; and having described the presently preferred mode and apparatus, the invention is not to be limited thereto.

What is claimed is:

1. An apparatus for forming a score line of predetermined configuration in synthetic plastic sheet material, the apparatus comprising:

a female die member and a male scoring member movable relative to one another into and out of score-forming relation, said female member having a surface with a slot for receiving said scoring member during score-forming, said scoring member having an end for locally stretching said sheet material into said slot during score-forming in order to form a score line in said sheet material without cutting completely through said material at said line,

means for moving said member into score-forming relation, and

means for immobilizing said sheet material between said members in those areas bordering said slot during said score-forming,

said means for immobilizing comprising a resilient material which frictionally engages and immobilizes said sheet material.

2. An apparatus for forming a score line of predetermined configuration in synthetic plastic sheet material which comprises:

a female die member and a male scoring member movable relative to one another into and out of score-forming relation,

said female die member having a surface with a slot therein for receiving said scoring member during score-forming,

said scoring member including a scoring rule for urging said sheet material into said slot during score-forming in order to form a score line in said sheet material without cutting completely through said material at said line,

said scoring member further including means for immobilizing said sheet material,

said immobilizing means comprising a resilient material extending along opposite sides of said rule, and above the scoring end of the rule and having sufficient resiliency for compression below the rule end when said members are brought into score-forming relation, said resilient material adapted to frictionally engage and immobilize said sheet material between said members in those areas bordering said slot during score-forming, and

means for moving said members into score-forming relation.

3. The apparatus of claim 2 wherein said male member further comprises a cutting blade having two sides and a' cutting end which cuts the sheet material when said members are moved into score-forming relation.

4. The apparatus of claim 3 further including resilient material extending along said cutting blade on both sides thereof and above the cutting end of said cutting blade, and having sufficient resiliency for compression below the cutting blade end when said members are brought into score-forming relation. I

5. The apparatus of claim 2 wherein said slot has a bottom and wherein said scoring rule is of sufficient dimension so that its end extends into said slot during score-forming and compresses said sheet material between said end and said bottom. 

1. An apparatus for forming a score line of predetermined configuration in synthetic plastic sheet material, the apparatus comprising: a female die member and a male scoring member movable relative to one another into and out of score-forming relation, said female member having a surface with a slot for receiving said scoring member during score-forming, said scoring member having an end for locally stretching said sheet material into said slot during score-forming in order to form a score line in said sheet material without cutting completely through said material at said line, means for moving said member into score-forming relation, and means for immobilizing said sheet material between said members in those areas bordering said slot during said score-forming, said means for immobilizing comprising a resilient material which frictionally engages and immobilizes said sheet material.
 2. An apparatus for forming a score line of predetermined configuration in synthetic plastic sheet material which comprises: a female die member and a male scoring member movable relative to one another into and out of score-forming relation, said female die member having a surface with a slot therein for receiving said scoring member during score-forming, said scoring member including a scoring rule for urging said sheet material into said slot during score-forming in order to form a score line in said sheet material without cutting completely through said material at said line, said scoring member further including means for immobilizing said sheet material, said immobilizing means comprising a resilient material extending along opposite sides of said rule, and above the scoring end of the rule and having sufficient resiliency for compression below the rule end when said members are brought into score-forming relatiOn, said resilient material adapted to frictionally engage and immobilize said sheet material between said members in those areas bordering said slot during score-forming, and means for moving said members into score-forming relation.
 3. The apparatus of claim 2 wherein said male member further comprises a cutting blade having two sides and a cutting end which cuts the sheet material when said members are moved into score-forming relation.
 4. The apparatus of claim 3 further including resilient material extending along said cutting blade on both sides thereof and above the cutting end of said cutting blade, and having sufficient resiliency for compression below the cutting blade end when said members are brought into score-forming relation.
 5. The apparatus of claim 2 wherein said slot has a bottom and wherein said scoring rule is of sufficient dimension so that its end extends into said slot during score-forming and compresses said sheet material between said end and said bottom. 